Audio coding is used in many applications and environments such as satellite radio, digital radio, internet streaming (web radio), digital music players, and a variety of mobile multimedia applications. There are many audio coding standards, such as standards according to the motion pictures expert group (MPEG), windows media audio (WMA), and standards by Dolby Laboratories, Inc. Many audio coding standards continue to emerge, including the MP3 standard and successors to the MP3 standard, such as the advanced audio coding (AAC) standard used in “iPod” devices sold by Apple Computer, Inc. Audio coding standards generally seek to achieve low bitrate, high quality audio coding using compression techniques. Some audio coding is “loss-less,” meaning that the coding does not degrade the audio signal, while other audio coding may introduce some loss in order to achieve additional compression.
In many applications, audio coding is used with video coding in order to provide multi-media content for applications such as video telephony (VT) or streaming video. Video coding standards according to the MPEC, for example, often use audio and video coding. The MPEG standards currently include MPEG-1, MPEG-2 and MPEG-4, but other standards will likely emerge. Other exemplary video standards include the International Telecommunications Union (ITU) H.263 standards, ITU H.264 standards, QuickTime™ technology developed by Apple Computer Inc., Video for Windows™ developed by Microsoft Corporation, Indeo™ developed by Intel Corporation, RealVideo™ from RealNetworks, Inc., and Cinepak™ developed by SuperMac, Inc. Some audio and video standards are open source, while others remain proprietary. Many other audio and video coding standards will continue to emerge and evolve.
Bitstream errors occurring in transmitted audio signals may have a serious impact on decoded audio signals due to the introduction of audible artifacts. In order to address this quality degradation, an error control block including an error detection module and a frame loss concealment (FLC) module may be added to a decoder. Once errors are detected in a frame of the received bitstream, the error detection module discards all bits for the erroneous frame. The FLC module then estimates audio data to replace the discarded frame in an attempt to create a perceptually seamless sounding audio signal.
Various techniques for decoder frame loss concealment have been proposed. However, most FLC techniques suffer from the extreme tradeoff between concealed audio signal quality and implementation cost. For example, simply replacing the discarded frame with silence, noise, or audio data of a previous frame represents one extreme of the tradeoff due to the low computational cost but poor concealment performance. Advanced techniques based on source modeling to conceal the discarded frame fall on the other extreme by requiring high or even prohibitive implementation costs to achieve satisfactory concealment performance.